urllib3 up to 2.5.x Streaming API data amplification

CVSS Meta Temp Score
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CTI Interest Score
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7.3$0-$5k0.00

Summaryinfo

A vulnerability identified as critical has been detected in urllib3 up to 2.5.x. This impacts an unknown function of the component Streaming API. Performing a manipulation results in data amplification. This vulnerability is reported as CVE-2025-66471. The attack is possible to be carried out remotely. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in urllib3 up to 2.5.x. This affects some unknown functionality of the component Streaming API. The manipulation with an unknown input leads to a data amplification vulnerability. CWE is classifying the issue as CWE-409. The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. This is going to have an impact on availability. The summary by CVE is:

urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.0 and prior to 2.6.0, the Streaming API improperly handles highly compressed data. urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When streaming a compressed response, urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). The library must read compressed data from the network and decompress it until the requested chunk size is met. Any resulting decompressed data that exceeds the requested amount is held in an internal buffer for the next read operation. The decompression logic could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This can result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2025-66471 since 12/02/2025. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 278513 (Ubuntu 20.04 LTS / 22.04 LTS / 24.04 LTS / 25.04 / 25.10 : urllib3 vulnerabilities (USN-7927-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 2.6.0 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (278513) and CERT Bund (WID-SEC-2025-2927). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

  • NetApp ActiveIQ Unified Manager

Productinfo

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 7.5
VulDB Meta Temp Score: 7.3

VulDB Base Score: 7.5
VulDB Temp Score: 7.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 7.5
NVD Vector: 🔒

CVSSv2info

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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Data amplification
CWE: CWE-409 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 278513
Nessus Name: Ubuntu 20.04 LTS / 22.04 LTS / 24.04 LTS / 25.04 / 25.10 : urllib3 vulnerabilities (USN-7927-1)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: urllib3 2.6.0

Timelineinfo

12/02/2025 CVE reserved
12/05/2025 +3 days Advisory disclosed
12/05/2025 +0 days VulDB entry created
01/03/2026 +29 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2025-66471 (🔒)
GCVE (CVE): GCVE-0-2025-66471
GCVE (VulDB): GCVE-100-334497
CERT Bund: WID-SEC-2025-2927 - NetApp ActiveIQ Unified Manager: Mehrere Schwachstellen ermöglichen Denial of Service

Entryinfo

Created: 12/05/2025 17:53
Updated: 01/03/2026 11:09
Changes: 12/05/2025 17:53 (65), 12/11/2025 03:51 (10), 12/13/2025 17:17 (2), 01/03/2026 11:09 (7)
Complete: 🔍
Cache ID: 216::103

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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